Television apparatus



Feb. 22, 1938.

A. KAROLUS 2,109,198

TELEVISION APPARATUS Filed March 23, 1935 AUGUST KAROLUS BY 7%. m

ATTORNEY Patented Feb. 22, 1938 UNlTED STATES FATEN'E GFFIQE TELEVISION APPARATUS August Karolus, Leipzig, Germany, assignor to Radio Corporation of Delaware America, a corporation of Claims.

This invention relates to television apparatus and to the method of transmission and reception of television signaling impulses. The transmission apparatus herein disclosed is of a type 5 which is particularly adapted for use in conjunction with the receiving apparatus shown and described in my copending application Serial No. 15,156, filed April 8, 1935 (filed in Germany as Serial No. K.l33,879 on April 19, 1934) although it is to be understood that the disclosure is in no way limited as to the particular form of the cooperating receiver device.

The invention is predicated upon the supposition and fact that for satisfactory television work, the fineness of scanning or resolution of the picture must correspond to a ruled plate or screen of 100 picture lines or better. In addition to developments in this direction designed so as to fulfill these requirements so far as the equipment and the transmission methods are concerned, i. e., of adapting ever increasing line numbers, a, marked expansion in the transmission range of electric telegraph channels has of late become noticeable. It is a fact that both on ultra short waves as well as on special cable lines frequency bands of cycles may be transmitted over satisfactory ranges of distance without the requirements respecting the provision of amplifier means being unduly severe. This fact places a different aspect upon the future and development of the television problem.

In the past, limitations were imposed upon every television development by the restricted frequency transmission range of telegraphic 35 channels, and the fineness of scanning, or in other words, the number of picture lines, had to be adapted to these resistance conditions. Hence, it was not usually feasible to go beyond comparatively coarse screens. With these coarse screens it was not any too difficult to transmit objects of moderate luminosity and to insure adequately bright received television pictures. When the demand for substantially finer screens became acute and inescapeable, it proved necessary in view of the unaltered or unimproved transmission ranges of telegraphic channels to connect a plurality of these in parallel so that a portion or component of the picture could be transmitted over each of these separate -channels. Today, however, there are means and ways known in the art making it possible to transmit on a single modulated carrier wave or over a single cable conductor the frequency band of a picture divided almost into any desired fine ness or any desired high number of lines,

This invention is based upon the last mentioned fact, and it is concerned with a television system in which, in accordance with what precedes, the picture modulation is conveyed from the sending to the receiving apparatus over a single modulated carrier wave or over a single conductor, Whereas at the sending or at the receiving points, or at both places, if necessary, simultaneous scanning and re-creation, as the case may be, of a multiplicity or plurality of picture elements takes place. What is thus secured, on the one hand, is such a great Working safety and reliability in transmission that it would be inobtainable in paralleling several telegraphic channels because of the difficulties associated with the balancing of the same.

On the other hand, because of the multiple scanning, it will be possible to transmit scenes and pictures of lower luminosity or with a greater line division than has heretofore been the case, while so far as reception is concerned, there are available the advantages residing in greater luminosity of the televised picture and in finer screening of the same. In fact, it is only in this manner that in the scanning, for instance, of living or moving persons the fineness of scanning which is nowadays demanded becomes feasible at all.

It is, fundamentally speaking, known in the art of television to subdivide the entire picture area or a single picture line so that each area is associated with a separate photocell and then to illuminate these cells simultaneously, while the evaluation of the photoelectric currents or voltages generated in them is accomplished in time sequence. However, in the arrangements previously suggested for this purpose serious difficulties arise inasmuch as, without exception, they cause the conversion of luminous values into an uninterrupted series or sequence of cur- 40 rent impulses directly from the photo-elements. Inasmuch as the voltages thus becoming active and operative, especially where the luminosity or brightness of the picture is poor, turn out to be extremely low, it follows that the stray or interference level is comparatively high. On the other hand, in case of a so-called picture mosaic, the high frequency of line change-over presupposes a low coupling resistance in the input of the modulation amplifier and thus, so far as the transmission process is concerned, an unfavorable relationship between the useful or working amplitude and the stray or interference level, not to mention this circumstance that for arrangements of this sort it is, for the time being, still impossible to insure adequate uniformity of photoelectric responsiveness throughout the whole line sequence by simple ways and means.

The present invention has therefore as one of its primary objects that of obviating these difiiculties and defects by reason of the fact that the scanning of luminous values occurring in time sequence along a picture line composed of individual photocells is not brought about with the vanishingly low individual potentials of these cells themselves as is usually the custom, but rather are brought about by an amplifier associated with each separate photocell so as to secure sufficient preliminary or input amplification of the signal amplitude. In this connection, far more favorable conditions respecting the stray or interference level as well as utilization of light are obtainable, not to speak of the chance of equalizing sensitivity disparities of the photoelectric cells simply by adjusting the sensitiveness or response of the various amplifiers.

The invention has been illustrated according to two preferred forms thereof by the accompanying drawing wherein Fig. 1 shows one suitable arrangement for accomplishing the aims and objects above set forth, and Fig. 2 shows a modified arrangement.

According to the invention, the optical transmitter causes the picture to be moved line by line over a linear row of photoelectric cells extending in the direction of the lines scanned and comprising a plurality of constituent photocells, the number of the latter being equal to the number of picture elements or elementary areas contained in a full line. For the purpose of considering the method of television in this case the number of separate points to be scanned may be denoted by the letter in. In order that the original picture may be scanned or resolved in the said manner, there is used, for instance, a projection device in conjunction with a mirror wheel which directs the light from each elemental strip of the subject to be scanned so that all of the p many points or picture points of a line are simultaneously scanned photoelectrically with the result that 29 many current and voltage values are produced.

These current and voltage values must be eval-- uated and utilized for the control of the transmitter during the length of time t available for scanning each picture line. For this purpose, a high speed inertialess switch means, Within time interval t, picks up p many different voltages (in sufliciently amplified form) and thus converts the transmission values available in time sequence into a series of corresponding telegraphic impulses.

Between each photoelectric cell and the corresponding scanning device which may be a switch photocell or contact of a cathode ray change-over switch means or distributor, to be discussed later, there is interposed a single-stage or multi-stage variable tube type amplifier having such a high grid resistance that the time constant of the input circuit is of the same order of magnitude as the line duration 15. By suitable adjustment of the gain of each amplifier a compensation of the sensitiveness disparities of each or" the p many photoelectric cells is insured. This arrangement makes it feasible to cause the photoelectric efiect produced from the picture point brightness, that is the luminosity of each elementary area of the subject, to be effective upon the various cells throughout the duration of a line t, with the consequence that the picture signals or impulses, which in themselves are several times stronger,

may by means of subsequent amplification be raised to such amplitudes that, even in the presence of lower brightness of the original picture and or" marked irregularity of sensitiveness in the p many scanning or pick-up photocells, very powerful and balanced picture impulses lying away above the stray level are obtained.

Because of the time-paralleled operation of the 29 many photelectric cells the maximum frequency of brightness change amounts then to only 1/t, whereas in the mode of scanning heretofore customary in the art it was p/t. As a result, it is feasible to raise the grid resistances on which the various cells operate, seeing that because of the reduced frequency of the photoelectric current harmful circuit capacitances no longer play the same harmful part as shunt resistances. Hence, the control voltage of the photocells is already multiplied at the input grid of the 10 many amplifiers, though it will be raised to useful values faithfully reproducing the brightness values only by the variable or gain-controlled individual amplifiers provided at points further along in the system.

The high speed switch free from inertia which is required both at the sending as well as at the receiving end according to this invention, which switch during the length of a line t picks up the transmission values of all elementary areas consecutively, may be of varied and different forms of construction. At the transmitter end of the system it is possible to cause an intense pencil of light of constant value to pass at a suitable rate of speed over a series of p many photoelectric switch cells which are conjugated to the p many scanning cells of the picture line or strip, i. e., the switches are suitably united with the output ends of the amplifiers controlled thereby so that by becoming transmissive or conductive for current as the pencil of light impinges thereon, volume regulated or dosed voltage impulses which are proportional to the different brightness values of the p many picture elements along the line or strip of the picture result. These sequential control impulses act through a series resistance common to all of the 10 many discharge paths upon the control grid of an electron tube which con stitutes the input of the transmitter amplifier. The releasing or scanning light ray pencil could be shifted over the lines by the agency of a mirror wheel arrangement of a kind known in the earlier art.

Other ways and means of operating a system of this type include substituting in the transmitter apparatus a cathode ray pencil for the light ray pencil. This cathode ray pencil or beam, by the aid of ways and means known in the prior art, is rotationally swept over a circular sequence or bank of circuit-making or closing contacts, the number of these latter equally the number p of elementary areas of the picture line. In a fundamentally similar manner the switching arrangement, as hereinbefore described, causes the conversion of the subsequently amplified potentials simultaneously created by the luminous actions in the 10 many scanning cells into a time sequence of impulses to control the television transmitter.

The switch action of the cathode ray pencil and photoelectric release action could also be combined in such a manner that the luminescence produced by the influence of the impinging elec trons in a phosphorescent surface is caused to act upon a bank or row of photocells disposed opposite the said screen. The preferable plan iii) is to guide the cathode ray pencil which is pref-. erably of constant and stable intensity along a circular path, it, of course, being the plan also that the photoelectric cells are to be disposed along the ensuing luminous track.

However, only a few of the conceivable and possible ways and means adapted to insure high speed scanning or pick-up of line values have been mentioned in what precedes. In other schemes for instance, the p many switch photoelectric cells, or the p many switch contacts of the cathode ray tube could be replaced by p many blocked electron tubes operated from the anode end by the amplified photocell potentials. In such a case the control grids of the electron tubes would have impressed thereon in time sequence brief unlocking positive voltage impulses. This might be accomplished, for instance, by the aid of a surge or traveling wave whose transit time along the p many control grids is equal to t, and whose periodic production is synchronized with the picture resolution or scanning. If the electron tubes are equipped with two multiplicatively acting control grids, as would be the case with the usual form of hexode tube, then the p many second control grids, in the presence of constant plate potential, may be fed directly or through amplifiers, with the brightness potentials created by the 11: many scanning cells. These will then govern the intensity prevailing at any given instant of the plate current impulse being amplified at the same time in accordance with the amplifier function of the tube incidental to the switch process, whereas the p many first grids merely fulfill the function of opening and closing or blocking the discharge path. All of the discharge current surges exercise a controlling action through a joint series resistance upon the input tube of the transmitter amplifier. The tube arrangement as here described, however, is capable of a great many modifications in accordance with rules and laws known in the art.

The re-conversion at the receiving end of the sequence of impulses sent from the transmitter end into a time parallel control of 110 many channels, fundamentally speaking, is accomplishable in accordance with the same scheme as at the sending end. In the receiver system a switch pencil which is modulated in its intensity by the electrical signals corresponds to the switch pencil of constant intensity at the transmitter end.

Reference may now be had more specifically to the forms of the invention exemplified and schematically illustrated by Figs. 1 and 2 of the drawing. Considering first Fig. 1, the pick-up photoelectric cells are indicated at l, 2, 3, 4 p. The varying light intensities of the projected picture line or strip are caused to impinge on these cells in the direction of the arrows. The numerals 5, 6, l, 8, etc., indicate the p many separately regulable amplifiers, while numerals 9, 10, ll, l2, etc., represent resistances whose voltage fall is governed by the excitation of the cells l, 2, 3, l while additional capacities, shown in dotted outline, if desired, may be shunted in relation to these resistances 9, Hi,

II, it

In the case of Fig. 1, the assumption is made that the high speed scanning of line values is eiTected by the aid of light. For this purpose, the free ends of the resistances 9, 16, ll, l2 with single-pole through-connection are united with the p many switch photocells L8, 2, 3', 4' 10' whose active cathodes are placed opposite the anodes connected together by lead l3.

Upon the switch photocells, in the direction of the arrows a, b, c", d r is caused to impinge the constant light flux of the optical changeover switch in such a way that the excitation propagating in the sense of the horizontal arrow A returns cyclically at a periodicity t, that is the length of a line of scanning. The photoelectrical discharge current impulses consecutively recurring at like time intervals t/p and being of variable amplitude flow through the joint resistance l5 and the return lead it, and the drop of potential caused across the resistance 15 controls the input tube It of the amplifier in the transmitter (not shown).

In a modified form of the arrangement shown by Fig. 2, the switch photocells l, 2', 3, etc., have been replaced. by the closing paths of a rotating cathode ray pencil 25, while the arrangement of the input of the transmitter amplifier, that is, the part comprising the conductor l3, the resistor l5 and the tube It, has remained unaltered. In this figure the numerals 9, H), ll, 52 again denote the output resistances of the amplifiers 5, 6, l, 8 (not again shown by Fig. 2) across which the photoelectrically controlled brightness voltages of a line of elementary areas or picture points result. The free ends of the resistances are united with the 10 many electrodes ll, l6, l9, 29 of the cathode ray tube to which are coordinated p many grid-like cooperating electrodes 2!, 22, 23, 24 placed opposite the former. These systems act like p many Faraday cages, the interior spaces of which are rendered conductive sequentially by the cathode ray pencil 25 penetrating therein. Each of these individual cells incidentally sets up a surge or impulse of current, the intensity of which is a function of the fall of potential prevailing at a given instant across the resistance (9, I0, ll, 52 coordinated thereto.

Having thus described the invention, what is claimed and desired to secure by Letters Patent is the following:

1. In a television system, a plurality of light translating elements positioned in line formation, an amplifier system connected with each. of said elements, said amplifiers each having a time constant circuit associated therewith in the order of the time duration of each scanning line, a load circuit, and an inertialess high speed switching device for sequentially connecting each amplifier with the load circuit.

2. In a television system, a plurality of light translating elements positioned in line formation, an amplifier system connected with each of said elements, each of said amplifier systems having a time constant circuit associated therewith in the order of the time duration of each scanning line of the subject of which an electro-optical representation is to be produced, a load circuit, a second light translating element serially connected with each of said first-named light translating elements, and an inertialess high speed switching device for sequentially connecting each amplifier with the load circuit.

3. The television system claimed in claim 2 wherein said inertialess high speed switching device consists of a light ray pencil caused to sweep across said second-named light translating elements.

4. The television system claimed in claim 1, wherein said inertialess high speed switching de vice consists of a cathode ray tube.

5. A television transmission system comprising a plurality of light translating elements positioned in line formation, an amplifier system connected with each of said elements, a time constant circuit associated with each of said amplifier systems having a time constant in the order of the time duration of each scanning line, a load circuit, a second light translating element connected in series with each of said amplifying devices and the load circuit, said second-named light translating elements being arranged in a closed circular path, and an electronic tube for sequentially illuminating each of said second-named light translating elements for connecting the first-named light translating elements and the shielded amplifiers in sequence With the load circuit.

AUGUST KAROLUS. 

